Physics & Astronomy ETDs

Ellery Strom

Publication Date

5-30-1966

Abstract

Scintillation spectrometer measurements were made of the x-ray spectra produced by a constant-potential x-ray unit operating at 100, 150, 200, 250, and 300 kV. An attempt was made to measure the absolute intensity as well as the spectral distribution. In order to reduce the counting rate to a measureable level, it was necessary to place the thallium-activated sodium-iodide detector 50 meters from the target. Since the air attenuation was quite large, measurements were made both in air and in helium. In order to contain the helium, an Orangeburg pipe was employed, and its effect on the spectra was determined by measurements in air with and without the pipe; the pipe introduced a slight shift in the spectra due to small-angle scatter. Small shifts in the spectra were also observed when the tube current was varied. The effect of varying the target and detector apertures was also investigated. The target aperture had little effect on the shape of the spectral distribution, but the absolute intensity decreased rapidly as the aperture size approached and became smaller than the target size. The intensity was found to vary directly with the area of the detector aperture. A rough estimate of the ratio of the intensity of the tungsten-K x rays to the continuum was made. The line-to-continuum ratio was 4% at an exciting potential of 100 kV, but increased to 30% at 150 kV and remained constant up to 300 kV. The measurements were compared to calculations based on the empirical relation of Kulenkampff. The calculations were converted into terms which would permit direct comparison with measurements. Thus, the calculated spectra were corrected for the inherent filtration of the x-ray tube and were adjusted to correspond to the distance, air and helium attenuation, detector aperture, counting time, and tube current actually employed in the measurements. The calculated spectra were also corrected for distortion by the detector because of Gaussian broadening of monoenergetic lines, partial energy deposition in the crystal, and the escape of iodine-K x rays. The hand calculation of the detector distortion was in good agreement with a Monte Carlo calculation of the crystal response spectrum. A comparison of measurement and calculation indicated that the best agreement was obtained when the proportionality constant in the equation for the x-ray production efficiency was 0.5 x 10-6 keV-1. Considering the many corrections that have to be applied, the agreement between measurement and calculation was on the whole reasonably good. However, the Kulenkampff equation does not include the characteristic radiation from the target, and it predicts significantly larger intensities in the 20 to 50 keV region than were actually measured.

Degree Name

Physics

Level of Degree

Masters

Department Name

Physics & Astronomy

First Committee Member (Chair)

Christopher Pratt Leavitt

Second Committee Member

John Root Green

Third Committee Member

Harvey Isreal

Language

English

Document Type

Thesis

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